Reactor servicing platform

ABSTRACT

A reactor servicing platform for a nuclear reactor is provided. The nuclear reactor includes a reactor pressure vessel positioned in a primary containment and at least one refuel bridge. The primary containment includes a refueling floor. The servicing platform, in an exemplary embodiment, includes a frame, a support structure, and a floor covering the frame. The floor includes a reactor access opening sized to permit access to the reactor pressure vessel.

BACKGROUND OF INVENTION

[0001] This invention relates generally to nuclear reactor, and moreparticularly to a service platform for use in a nuclear reactor.

[0002] A reactor pressure vessel (RPV) of a boiling water reactor (BWR)typically has a generally cylindrical shape and is closed at both ends,e.g., by a bottom head and a removable top head. A top guide, sometimesreferred to as a grid is spaced above a core plate within the RPV. Acore shroud, or shroud, surrounds the core plate and is supported by ashroud support structure. The core shroud is a reactor coolant flowpartition and structural support for the core components. Particularly,the shroud has a generally cylindrical shape and surrounds both the coreplate and the top guide. A removable shroud head is coupled to a shroudhead flange at the top of the shroud.

[0003] During refueling of a nuclear reactor, the majority of theservicing operations are performed from a bridge system that spans therefueling floor and the reactor and fuel storage pool cavities. Thesebridges typically have a straight four to eight foot wide walkway alongtheir length and can be positioned above the reactor or refueling poolcavity. To clear the hand rails and other structures at the edge of thereactor cavity or service pools, the refuel bridge must be elevatedabout five feet above the floor surface.

[0004] In use, the bridge is moved to the desired position above thereactor and personnel work along the walkway of the bridge. When workingover a round reactor vessel such as a boiling water reactor, access to aspecific azimuth zone of the round reactor vessel is restricted for anygiven placement of the bridge because of shape of the bridge. Withexisting bridge access, the number of work activities, and number ofpersonnel that can perform work at the same time is limited. The use ofrefuel bridges and auxiliary bridges is the most efficient known methodof work access for achieving productivity for plant outage schedules.

[0005] The type of work required to service a nuclear plant would beenhanced by access to the reactor along the radial and tangentialdirections of the vessel or component. A normal bridge system can onlyaccomplish radial or tangential alignment at the specific azimuthpositions of 0, 90, 180, or 270 degrees. Radial and tangential alignmentcan never be accomplished simultaneously. Therefore, personnel andequipment may not have the optimal angle of access for visualobservation or equipment manipulation.

SUMMARY OF INVENTION

[0006] In one aspect, a reactor servicing platform for a nuclear reactoris provided. The nuclear reactor includes a reactor pressure vesselpositioned in a primary containment and at least one refuel bridge. Theprimary containment includes a refueling floor, and the servicingplatform includes a frame, a support structure, and a floor covering theframe. The floor includes a reactor access opening sized to permitaccess to the reactor pressure vessel.

[0007] In another aspect, a nuclear reactor is provided that includes aprimary containment vessel, a reactor pressure vessel positioned in theprimary containment vessel, and a reactor servicing platform. Theservicing platform includes a frame, a support structure, and a floorcovering the frame. The floor includes a reactor access opening sized topermit access to the reactor pressure vessel.

[0008] In another aspect, a method of servicing a nuclear reactor duringa reactor outage is provided. The reactor includes a primary containmentvessel and a reactor pressure vessel positioned in the primarycontainment vessel. The method includes positioning a servicing platformabove the reactor pressure vessel, and performing predeterminedservicing operations on the reactor. The servicing platform includes aframe, a support structure, and a floor attached to the frame. The floorincludes a reactor access opening sized to permit access to the reactorpressure vessel.

BRIEF DESCRIPTION OF DRAWINGS

[0009]FIG. 1 is simplified schematic view of a nuclear reactor.

[0010]FIG. 2 is a perspective schematic view of a reactor servicingplatform in accordance with an embodiment of the present invention.

[0011]FIG. 3 is a side schematic view of the reactor servicing platformshown in FIG. 2.

[0012]FIG. 4 is a bottom perspective view of the reactor servicingplatform shown in FIG. 2.

[0013]FIG. 5 is a top perspective schematic view of a reactor servicingplatform in accordance with an embodiment of the present invention.

[0014]FIG. 6 is a side schematic view of a reactor servicing platform inaccordance with an embodiment of the present invention.

[0015]FIG. 7 is a side schematic view of a reactor servicing platform inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

[0016] A reactor servicing platform having a reactor access opening topermit access to the reactor internal components during refueling andmaintenance outage operations is described below in detail. The reactorservicing platform permits multiple work crews and equipment tosimultaneously perform tasks at multiple azimuth locations around areactor vessel. The reactor servicing platform is fabricated from anysuitable material(s), for example, aluminum, steel, and thermoplasticand fiber composite materials. Further, the reactor servicing platformhas a modular design with major components sized for transport to areactor refuel floor through an equipment hatch. The reactor servicingis assembled in site in the reactor and can be disassembled andtransported to another reactor.

[0017] Referring specifically to the drawings, FIG. 1 is simplifiedschematic view of a nuclear reactor 10. Reactor 10 includes a reactorpressure vessel 12 positioned in a containment vessel 14. Reactorpressure vessel 12 has a generally cylindrical shape and includes abottom head 16 and a removable top head (not shown). A reactor core 18is located inside pressure vessel 12. A plurality of control rod drives20 extend through bottom head 16 and control the position of the controlrods (not shown) in core 18 which adjusts the reactivity of core 18.

[0018] Containment vessel 14 includes a drywell 22 in which pressurevessel 12 is located, and a wetwell 24. A refuel floor 26 extends from aside wall 28 of containment 14 and is located above pressure vessel 12.Refuel floor 26 permits worker access to pressure vessel 12 through anaccess opening 30 to perform refueling, maintenance, and other servicingfunctions of pressure vessel 12. A ledge 32 extends from refuel floor 26into access opening 30. Crane rails 34 are located on an upper surface36 of refuel floor 26.

[0019]FIG. 2 is a perspective schematic view of a reactor servicingplatform 38 in accordance with an embodiment of the present invention.FIG. 3 is a side schematic view of reactor servicing platform 38, andFIG. 4 is a bottom perspective view of reactor servicing platform 38.Referring to FIGS. 2, 3, and 4, servicing platform 38 servicing platform38 includes a frame 40, a support structure 42, and a floor 44 coveringframe 40. Floor 44 is formed from a plurality of floor panels 46attached to frame 40. Floor 44 includes a reactor access opening 48sized to permit access to reactor pressure vessel 12. At least oneauxiliary platform 50 (two shown) extends into access opening 48. Eachauxiliary platform 50 is movable along a perimeter of access opening 48.Access opening 48 can be any suitable shape, for example, a circular,elliptical, or polygonal shape. A safety rail or fence 52 extends arounda perimeter of access opening 48. Further, a safety rail or fence 54extends around an outer perimeter of floor 44. In alternate embodiments,reactor servicing platform 38 also includes servicing tools, forexample, lifting devices, that are movable along a perimeter of accessopening 48.

[0020] Frame 40 includes a plurality of beams 56, a circular centralbeam 58 and a plurality of cross-members 60 extending between beams 56and central beam 58. Circular central beam 58 defines reactor accessopening 48. Floor panels 46 attach to beams 56, central beam 58, andcross-members 60 to form floor 44. Auxiliary platforms 50 movably coupleto upper and lower support rails 62 and 64 that are coupled to circularcentral beam 58. Upper support rail 62 is coupled to central beam 58 bysupport brackets 66. Auxiliary platforms 50 include upper rollers 68 andlower rollers 70 that couple to upper and lower support rails 62 and 64respectively and permit auxiliary platforms 50 to move along supportrails 62 and 64 for positioning within reactor access opening 48. In analternate embodiment, servicing tools, for example, lifting devices, aremovably coupled to upper and lower support rails 62 and 64. Supportstructure 42 includes support pods 72 attached to frame 40. In oneembodiment support pods rest on upper surface 36 of refuel floor 26 tosupport servicing platform 38 over pressure vessel 12.

[0021]FIG. 5 is a top perspective schematic view of a reactor servicingplatform 74 in accordance with another embodiment of the presentinvention. Servicing platform 74 is substantially similar to servicingplatform 38, shown in FIGS. 2, 3, and 4, and components in servicingplatform 74 that are identical to components of servicing platform 38are identified in FIG. 5 using the same reference numerals used in FIGS.2, 3, and 4. Servicing platform 74 includes a frame 40, a floor 44covering frame 40, and a support structure 76. Floor 44 includes areactor access opening 48 sized to permit access to reactor pressurevessel 12. An auxiliary platform 78 is movably coupled to frame 40 andextends across the diameter of access opening 48.

[0022] Auxiliary platform 78 is movable around the perimeter of accessopening 48. Support structure 76 attaches to existing reactor bridges 80and 82 to suspend servicing platform 74 above reactor pressure vessel 12(shown in FIG. 1).

[0023]FIG. 6 is a side schematic view of a reactor servicing platform 84in accordance with an embodiment of the present invention. Servicingplatform 84 is substantially similar to servicing platform 38, shown inFIGS. 2, 3, and 4, and components in servicing platform 84 that areidentical to components of servicing platform 38 are identified in FIG.6 using the same reference numerals used in FIGS. 2, 3, and 4. Servicingplatform 84 includes a frame 40, a floor 44 covering frame 40, and asupport structure 86. Support structure 86 includes support pods 88attached to frame 40. Support pods 88 are sized and positioned to reston ledge 32 extending around access opening 30 in refuel floor 26 tosupport servicing platform 84 over pressure vessel 12 (shown in FIG. 1).

[0024]FIG. 7 is a side schematic view of a reactor servicing platform 90in accordance with an embodiment of the present invention. Servicingplatform 90 is substantially similar to servicing platform 38, shown inFIGS. 2, 3, and 4, and components in servicing platform 90 that areidentical to components of servicing platform 38 are identified in FIG.7 using the same reference numerals used in FIGS. 2, 3, and 4. Servicingplatform 90 includes a frame 40, a floor 44 covering frame 40, and asupport structure 92. Support structure 92 includes support members 94attached to frame 40. Each support member 94 includes wheels 96 sized toengage and roll on crane rails 34 (shown in FIG. 1) attached to refuelfloor upper surface 36 (shown in FIG. 1).

[0025] The above described servicing platforms 38, 74, 84, and 90,permit access to the reactor along the radial and tangential directionsof the vessel or component. The above described servicing platforms 38,74, 84, and 90 permit radial and tangential alignment simultaneously.Further, the above described servicing platforms 38, 74, 84, and 90improve plant outage schedules, work productivity, and quality byproviding a work platform that permits multiple work crews and equipmentto simultaneously perform tasks at multiple azimuths around a reactorvessel.

[0026] While the invention has been described in terms of variousspecific embodiments, those skilled in the art will recognize that theinvention can be practiced with modification within the spirit and scopeof the claims.

1. A reactor servicing platform for a nuclear reactor, the nuclearreactor comprising a reactor pressure vessel positioned in a primarycontainment and at least one refuel bridge, the primary containmentcomprising a refueling floor, said servicing platform comprising: aframe; a support structure; a floor covering said frame, said floorcomprising a reactor access opening sized to permit access to thereactor pressure vessel.
 2. A reactor servicing platform in accordancewith claim 1 further comprising at least one auxiliary platformextending into said access opening.
 3. A reactor servicing platform inaccordance with claim 2 wherein said at least one auxiliary platform ismovable along a perimeter of said access opening of said floor.
 4. Areactor servicing platform in accordance with claim 1 wherein saidaccess opening has a circular, elliptical, or polygonal shape.
 5. Areactor servicing platform in accordance with claim 1 further comprisinga safety rail extending around a perimeter of said access opening.
 6. Areactor servicing platform in accordance with claim 1 further comprisinga safety rail extending around an outer perimeter of said floor.
 7. Areactor servicing platform in accordance with claim 1 wherein said floorcomprises at least one floor panel coupled to said platform frame.
 8. Areactor servicing platform in accordance with claim 1 wherein saidservicing platform comprises at least one of steel, aluminum, and athermoplastic and fiber composite material.
 9. A reactor servicingplatform in accordance with claim 1 wherein said support structure isconfigured to suspend said servicing platform from two spaced apartrefuel bridges.
 10. A reactor servicing platform in accordance withclaim 1 wherein said support structure comprises a plurality of wheelssized to engage a crane rail.
 11. A reactor servicing platform inaccordance with claim 1 wherein said support structure is configured toengage the refueling floor of the reactor.
 12. A reactor servicingplatform in accordance with claim 1 further comprising at least onelifting device movably coupled to said frame, said at least one liftingdevice movable along a perimeter of said access opening.
 13. A nuclearreactor comprising: a primary containment vessel; a reactor pressurevessel positioned in said primary containment vessel; and a reactorservicing platform comprising: a frame; a support structure; a floorcovering said frame, said floor comprising a reactor access openingsized to permit access to said reactor pressure vessel.
 14. A nuclearreactor in accordance with claim 13 wherein said servicing platformfurther comprises at least one auxiliary platform extending into saidaccess opening.
 15. A nuclear reactor in accordance with claim 13wherein said at least one auxiliary platform is movable along aperimeter of said access opening of said floor.
 16. A nuclear reactor inaccordance with claim 13 wherein said servicing platform access openinghas a circular, elliptical, or polygonal shape.
 17. A nuclear reactor inaccordance with claim 13 wherein said servicing platform floor comprisesat least one floor panel coupled to said platform frame.
 18. A nuclearreactor in accordance with claim 13 wherein said servicing platformcomprises at least one of steel, aluminum, and a thermoplastic and fibercomposite material.
 19. A nuclear reactor in accordance with claim 13further comprising at least two refuel bridges spaced apart andpositioned above said reactor pressure vessel, said servicing platformsupport structure engaging said refuel bridges to suspend said servicingplatform from two spaced apart refuel bridges.
 20. A nuclear reactor inaccordance with claim 13 wherein said primary containment comprises arefuel floor located above said pressure vessel, said refuel floorcomprising a plurality of crane rails, said support structure comprisinga plurality of wheels sized to engage said crane rails.
 21. A nuclearreactor in accordance with claim 13 wherein said primary containmentcomprises a refueling floor located above said pressure vessel, saidservicing platform support structure engaging said refueling floor tosupport said servicing platform above said pressure vessel.
 22. Anuclear reactor in accordance with claim 21 wherein said refuel floorcomprising a pressure vessel access opening and a ledge extendingcircumferentially around said pressure vessel access opening, saidservicing platform support structure engaging said ledge to support saidservicing platform above said pressure vessel.
 23. A nuclear reactor inaccordance with claim 13 wherein said servicing platform furthercomprises at least one lifting device movably coupled to said frame,said at least one lifting device movable along a perimeter of saidaccess opening.
 24. A method of servicing a nuclear reactor during areactor outage, the reactor comprising a primary containment vessel anda reactor pressure vessel positioned in the primary containment vessel,said method comprising: positioning a servicing platform above thereactor pressure vessel, the servicing platform comprising a frame, asupport structure, and a floor attached to the frame, the floorcomprising a reactor access opening sized to permit access to thereactor pressure vessel; and performing predetermined servicingoperations on the reactor.
 25. A method accordance with claim 24 whereinthe servicing platform further comprises at least one auxiliary platformextending into the access opening.
 26. A method in accordance with claim24 wherein the at least one auxiliary platform is movable along aperimeter of the access opening of said floor.
 27. A method inaccordance with claim 24 wherein the servicing platform access openinghas a circular, elliptical, or polygonal shape.
 28. A method inaccordance with claim 24 wherein the servicing platform comprises atleast one of steel, aluminum, and a thermoplastic and fiber compositematerial.
 29. A method in accordance with claim 24 wherein the reactorcomprises at least two refuel bridges spaced apart and located in theprimary containment above the reactor pressure vessel, and positioning aservicing platform above the reactor pressure vessel comprisespositioning the servicing platform with the servicing platform supportstructure engaging the refuel bridges to suspend the servicing platformfrom the two spaced apart refuel bridges.
 30. A method in accordancewith claim 24 wherein the primary containment comprises a refuel floorlocated above the pressure vessel, the refuel floor comprising aplurality of crane rails, the support structure comprising a pluralityof wheels, and positioning a servicing platform above the reactorpressure vessel comprises positioning the servicing platform with theservicing platform support structure wheels engaging the crane rails.31. A method in accordance with claim 24 wherein the primary containmentcomprises a refueling floor located above the pressure vessel, andpositioning a servicing platform above the reactor pressure vesselcomprises positioning the servicing platform with the servicing platformsupport structure engaging the refueling floor to support the servicingplatform above the pressure vessel.
 32. A method in accordance withclaim 31 wherein the refuel floor comprises a pressure vessel accessopening and a ledge extending circumferentially around the pressurevessel access opening, and positioning a servicing platform above thereactor pressure vessel comprises positioning the servicing platformwith the servicing platform support structure engaging the ledge tosupport the servicing platform above the pressure vessel.
 33. A methodin accordance with claim 24 wherein the servicing platform furthercomprises at least one lifting device movably coupled to the frame, theat least one lifting device movable along a perimeter of the accessopening.